Use the "4 corner rule" - meaning - refer to the lease. If it's a TAR lease agreement go to paragraph 28 and reference that section. As a property management company owner / broker (and former Army officer) - I know the laws on both sides.
The early termination clause for military only applies for PCS or TDY + 90 day orders. You have seen this before and should be no surprise.
For buying a house in the local area - go with what Para 28 says and DO NOT DEVIATE.
Why? Federal Fair Housing laws say that you can not discriminate against certain classes. The flip side of that is showing favorites to a class of people. Stick to the lease.
Want a better example? Offering a military discount on a rental home is a violation of Federal Fair Housing Laws. You are showing favortism to a certain class of people. Sounds rough, but it's true as we have had the experts from the Fair Housing Offices tell us this as that is how they interpret the laws. If you stick by the lease agreement as written, you will keep you and your property manger out of hot water.
The tenants may not like it - but they should have considered that when buying a home. Have them go squeeze the seller for concessions to offset their lease breaking fees.
Good luck out there!